Long-term coupled effects of hydrological factors on kinematic responses of a reactivated landslide in the Three Gorges Reservoir

A reservoir-induced landslide is a common geomorphological problem in the TGR (Three Gorges Reservoir) region, China. This study considers the Quchi landslide as an example of a large-scale partially reactivated ancient landslide in the TGR region; the possible kinematic responses and corresponding triggering mechanisms are investigated by analyzing eight-year monitoring data sets, field surveys, observations, and laboratory tests. The reactivated zone is primarily located in the south-western part of the ancient landslide, and it mainly moves along the deep sliding surface. The long-term monitoring data sets show that the presence of faster movements from June to September (rainy season), followed by slower deformation in the remaining nine months of the hydrological year. Both strong rainfall and drawdown during the low period of RWL (reservoir water level) are important hydrological factors responsible for the occurrence of faster movements. An RWL of 160 m a.s.l. (above sea level) during drawdown is considered the key water level for the initiation of faster movements. The motion pattern is primarily retrogressive, and the displacement velocity increases towards the toe. At present, the stability of the reactivated zone is indeterminate; a multistage failure with significant retrogressive evolution can possibly occur in the future. The findings in this study can help in managing reservoir landsides and designing landslide reinforcements in the regions of the word with geological settings similar to that of the TGR region.